file upload

文件上传漏洞,攻击者可以通过上传木马获取服务器的webshell权限。

文件上传漏洞的利用是

够成功上传木马文件，
其次上传文件必须能够被执行，
最后就是上传文件的路径必须可知。

同时做文件上传时，也需要了解中国菜刀的原理

Low

源码

<?php 

if( isset( $_POST[ 'Upload' ] ) ) {

    // Where are we going to be writing to?

    $target_path  = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/";

    $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] ); 

    // Can we move the file to the upload folder?

    if( !move_uploaded_file( $_FILES[ 'uploaded' ][ 'tmp_name' ], $target_path ) ) {

        // No

        echo '<pre>Your image was not uploaded.</pre>';

    }

    else {

        // Yes!

        echo "<pre>{$target_path} succesfully uploaded!</pre>";

    }

} 

?>

basename(path,suffix)

函数返回路径中的文件名部分，如果可选参数suffix为空，则返回的文件名包含后缀名，反之不包含后缀名

medium

源码

<?php 

if( isset( $_POST[ 'Upload' ] ) ) {

    // Where are we going to be writing to?

    $target_path  = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/";

    $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] ); 

    // File information

    $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ];

    $uploaded_type = $_FILES[ 'uploaded' ][ 'type' ];

    $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ]; 

    // Is it an image?

    if( ( $uploaded_type == "image/jpeg" || $uploaded_type == "image/png" ) &&

        ( $uploaded_size < 100000 ) ) { 

        // Can we move the file to the upload folder?

        if( !move_uploaded_file( $_FILES[ 'uploaded' ][ 'tmp_name' ], $target_path ) ) {

            // No

            echo '<pre>Your image was not uploaded.</pre>';

        }

        else {

            // Yes!

            echo "<pre>{$target_path} succesfully uploaded!</pre>";

        }

    }

    else {

        // Invalid file

        echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';

    }

} 

?>

Medium级别的代码对上传文件的类型、大小做了限制，要求文件类型必须是jpeg或者png，大小不能超过100000B

做法 ：文件包含+文件上传

high

源码

<?php 

if( isset( $_POST[ 'Upload' ] ) ) {

    // Where are we going to be writing to?

    $target_path  = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/";

    $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] ); 

    // File information

    $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ];

    $uploaded_ext  = substr( $uploaded_name, strrpos( $uploaded_name, '.' ) + 1);

    $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ];

    $uploaded_tmp  = $_FILES[ 'uploaded' ][ 'tmp_name' ]; 

    // Is it an image?

    if( ( strtolower( $uploaded_ext ) == "jpg" || strtolower( $uploaded_ext ) == "jpeg" || strtolower( $uploaded_ext ) == "png" ) &&

        ( $uploaded_size < 100000 ) &&

        getimagesize( $uploaded_tmp ) ) { 

        // Can we move the file to the upload folder?

        if( !move_uploaded_file( $uploaded_tmp, $target_path ) ) {

            // No

            echo '<pre>Your image was not uploaded.</pre>';

        }

        else {

            // Yes!

            echo "<pre>{$target_path} succesfully uploaded!</pre>";

        }

    }

    else {

        // Invalid file

        echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';

    }

} 

?>

strrpos(string,find,start)

函数返回字符串find在另一字符串string中最后一次出现的位置，如果没有找到字符串则返回false，可选参数start规定在何处开始搜索。

getimagesize(string filename)

函数会通过读取文件头，返回图片的长、宽等信息，如果没有相关的图片文件头，函数会报错。

可以看到，High级别的代码读取文件名中最后一个”.”后的字符串，期望通过文件名来限制文件类型，因此要求上传文件名形式必须是”.jpg”、”.jpeg” 、”*.png”之一。同时，getimagesize函数更是限制了上传文件的文件头必须为图像类型

做法：%00截断

impossible

源码

<?php 

if( isset( $_POST[ 'Upload' ] ) ) {

    // Check Anti-CSRF token

    checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' ); 

    // File information

    $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ];

    $uploaded_ext  = substr( $uploaded_name, strrpos( $uploaded_name, '.' ) + 1);

    $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ];

    $uploaded_type = $_FILES[ 'uploaded' ][ 'type' ];

    $uploaded_tmp  = $_FILES[ 'uploaded' ][ 'tmp_name' ]; 

    // Where are we going to be writing to?

    $target_path   = DVWA_WEB_PAGE_TO_ROOT . 'hackable/uploads/';

    //$target_file   = basename( $uploaded_name, '.' . $uploaded_ext ) . '-';

    $target_file   =  md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;

    $temp_file     = ( ( ini_get( 'upload_tmp_dir' ) == '' ) ? ( sys_get_temp_dir() ) : ( ini_get( 'upload_tmp_dir' ) ) );

    $temp_file    .= DIRECTORY_SEPARATOR . md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext; 

    // Is it an image?

    if( ( strtolower( $uploaded_ext ) == 'jpg' || strtolower( $uploaded_ext ) == 'jpeg' || strtolower( $uploaded_ext ) == 'png' ) &&

        ( $uploaded_size < 100000 ) &&

        ( $uploaded_type == 'image/jpeg' || $uploaded_type == 'image/png' ) &&

        getimagesize( $uploaded_tmp ) ) { 

        // Strip any metadata, by re-encoding image (Note, using php-Imagick is recommended over php-GD)

        if( $uploaded_type == 'image/jpeg' ) {

            $img = imagecreatefromjpeg( $uploaded_tmp );

            imagejpeg( $img, $temp_file, 100);

        }

        else {

            $img = imagecreatefrompng( $uploaded_tmp );

            imagepng( $img, $temp_file, 9);

        }

        imagedestroy( $img ); 

        // Can we move the file to the web root from the temp folder?

        if( rename( $temp_file, ( getcwd() . DIRECTORY_SEPARATOR . $target_path . $target_file ) ) ) {

            // Yes!

            echo "<pre><a href='${target_path}${target_file}'>${target_file}</a> succesfully uploaded!</pre>";

        }

        else {

            // No

            echo '<pre>Your image was not uploaded.</pre>';

        } 

        // Delete any temp files

        if( file_exists( $temp_file ) )

            unlink( $temp_file );

    }

    else {

        // Invalid file

        echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';

    }

} 

// Generate Anti-CSRF token

generateSessionToken(); 

?>

in_get(varname)

函数返回相应选项的值

imagecreatefromjpeg ( filename )

函数返回图片文件的图像标识，失败返回false

imagejpeg ( image , filename , quality)

从image图像以filename为文件名创建一个JPEG图像，可选参数quality，范围从 0（最差质量，文件更小）到 100（最佳质量，文件最大）。

imagedestroy( img )

函数销毁图像资源

DVWA各等级文件上传漏洞的相关教程结束。